The present invention relates to a coaxial connector and a method for manufacturing the coaxial connector, and a superconductor device and a method for manufacturing the superconductor device.
Superconductor filters using superconductor are recently much noted because of the good frequency characteristics in comparison with the general filters using electric good conductor.
The superconductor filter is used, loaded in a metal package which can shield the radio frequency from electromagnet and cooled down to about 70 K with, e.g., a freezer.
The proposed superconductor device with a superconductor filter mounted on will be explained with reference to FIG. 11. FIG. 11 is a sectional view of the proposed superconductor device.
As illustrated in FIG. 11, the superconductor filter 126 is mounted in a metal package 124. The superconductor filter 126 comprises a dielectric substrate 128, patterns 130 of a superconductor film formed on the dielectric substrate 128, and a ground plane 136 formed below the dielectric substrate 128. An electrode 134 is formed on the end of the pattern 130, and a ground electrode 138 is formed below the ground plane 136.
A coaxial connector 110 for electrically connecting a coaxial cable (not illustrated) and the superconductor filter 126 is disposed on the end of the metal package 124. The coaxial connector 110 functions as a receptacle. The coaxial connector 110 comprises a terminal 112 which is the core conductor, an insulator 114, a coupling 116 and a body 118.
A surface coating layer 120 of, e.g., In (indium) is formed on the surface of the terminal 112. The terminal 112 of the coaxial connector 110 is connected to the electrode 134 of the superconductor filter 126 with In-based solder 142.
The In-based solder 142 is used to connect the terminal 112 of the coaxial connector 110 and the electrode 134 of the superconductor filter 126 to each other because the In-based solder 142 can have good flexibility not only at the room temperature but also at low temperatures. When the terminal of the coaxial connector and the electrode of the superconductor filter are connected to each other with the usual Sn-37% Pb solder, with the temperature changed between the room temperature and low temperatures, large stresses are applied to the solder junction due to thermal expansion coefficient differences between the metal package 124 and the superconductor filter 126, and the solder junction is released. However, In-based solder, which has flexibility at the room temperature and low temperatures, can mitigate stresses applied to the solder junction due to the thermal expansion coefficient difference between the metal package 124 and the superconductor filter 126 even when the temperature is changed between the room temperature and low temperatures.
The proposed superconductor device permits the coaxial cable (not illustrated) and the superconductor filter 126 to be electrically connected to each other by using the coaxial connector 110, which facilitates the operation of connecting devices and instruments.
Following references disclose the background art of the present invention.
[Patent Reference 1]
Specification of Japanese Patent Application Unexamined Publication No. 2003-282197
However, to connect the terminal 112 of the coaxial connector 110 and the electrode 134 of the superconductor filter 126 to each other with the In-based solder 142, thermal processing must be made at a temperature higher than about 157° C., which is the melting point of In. The temperature of the thermal processing is set at, e.g., about 200° C. The thermal processing is made at a temperature sufficiently higher than the melting point of In so as to quickly and surely connect the terminal 112 and the electrode 134 to each other with the In-based solder 142. When the thermal processing is made at such relatively high temperature, there is a risk that oxygen might be discharged from the superconductor films 130, 136 of the superconductor filter 126. When oxygen is discharged from the superconductor films 130, 136, the critical temperature TC of the superconductor films 130, 136 of the superconductor filter 126 is lowered. When the critical temperature TC is lowered, the superconductor filter 126 must be cooled at a temperature lower than the lowered critical temperature TC, and the freezer is much loaded.